This invention relates generally to three dimensional nonwoven webs consisting of thermoplastic fibers, and more particularly concerns such webs which are formed from blends of polypropylene and polybutylene.
Nonwoven webs formed of thermoplastic fibers are well-known in the art and have found uses in a variety of applications. In one application, such nonwoven webs are formed by melt-blowing and are used as disposable industrial wipers. Such industrial wipers find application in numerous manufacture and maintenance facilities where personnel find it necessary to wipe up oil, grease, and water from a variety of surfaces. One such wiper made of melt-blown polypropylene fibers is manufactured and sold by Kimberly-Clark Corporation, the assignee of the present invention, under the trademark Kimtex.RTM..
Melt-blown nonwoven wipers of polypropylene thermoplastics fibers have advantage over cloth wipers in being cost effectively disposable with similar wiping characteristics as compared to cloth. Particularly, industrial wipers must be able to quickly pick up spilled liquids, both oil based and water based, and leave a clean, streak free surface. In addition, the wipers must have sufficient capacity to hold such liquids within the wiper structure until it is desired to remove the liquid by pressure such as by wringing.
Nonwoven melt-blown industrial wipers formed from polypropylene in the past have performed adequately in terms of their wiping characteristics, particularly with respect to oil and, when treated with a surfactant, with respect to water. Moreover, nonwoven industrial wipers made of polypropylene fibers have exhibited resistance to most commercially available solvents.
A superior three dimensional nonwoven melt-blown wiper, however, could be achieved by increasing strength, increasing toughness, and increasing tear resistance. A three dimensional nonwoven web is described in U.S. Pat. No. 4,741,941, to Englebert et al, which is incorporated herein by reference.
As described therein a three dimensional fabric is defined by a pattern of hollow projections extending out of the base plane of the web wherein the fibers or filaments are more aligned than in the land areas between the projections. The projections average in the range generally of from about 1 per square centimeter to about 80 per square centimeter, and they have an average height measured from the base plane to the most extended fibers within the range generally of from about 0.3 millimeters to 25 millimeters. The web is further characterized by an average bulk density in the range generally of from about 0.001 g/cc to about 0.11 g/cc. The fiber diameter may vary generally from about 1 micron to about 100 microns. Other important parameters include the variation in fiber alignment between the web land and projection areas. The projections include fibers or filaments with an average alignment of at least 5.degree. greater than the average alignment of the fibers or filaments in the land areas. Also the webs may be characterized by a volume ratio of volume of the projections to volume contained between the projections in both cases measured between planes at the base and the tops of the projections, in the range of from about 1 to 250. However, the web described in Englebert et al does not teach the increased strength which characterizes a superior three dimensional nonwoven melt-blown wiper.